In wireless communication systems, including New Radio (NR, sometimes referred to as 5G) and likely beyond, user equipment computes channel estimates based on pilot or reference signals, and computes the parameters needed for channel state information (CSI) reporting. A CSI report is sent from the user equipment to a network device via a feedback channel on request from the network, or the user equipment may be configured to send the CSI report periodically. A network scheduler uses this information in choosing the parameters for scheduling of this particular user equipment. The network sends the scheduling parameters to the user equipment in a downlink control channel. After that, actual data transfer takes place from the network to the user equipment.
When user equipment receives a packet, the user equipment returns a hybrid automatic repeat request-acknowledgement (HARQ-ACK) on the physical uplink control channel (PUCCH) to the network device/gNodeB. The gNodeB needs to correctly decode the HARQ-ACK from the PUCCH information to know whether the packet it transmitted was received correctly or not. Once the gNodeB decodes the PUCCH information, the gNodeB determines whether to retransmit the packet (if NACK) or pass it to upper layers (if ACK).
However, the PUCCH transmissions from multiple sets of user equipment increase the uplink interference level (or more specifically rise over thermal (RoT)) received in uplink at the gNodeB. This is because in uplink, each user equipment transmits on the same resources; (users are separated by non-orthogonal scrambling codes also referred to as Constant Amplitude Zero AutoCorrelation waveform or CAZAC sequences). Therefore uplink transmissions have to share interference-limited radio resources.
One way to improve PUCCH performance and thereby improve the PUCCH coverage is to repeat the HARQ-ACK transmission for each received packet, such as when a user equipment is at the cell edge, when the path loss is very high and/or when the received signal-to-noise ratio is very low. This is accomplished by the use of a HARQ-ACK repetition factor, which describes how many times the user equipment is to transmit the (same) HARQ-ACK message associated with a transport block. However when the HARQ-ACK is repeated, the network cannot schedule the user equipment in consecutive time intervals, because the user equipment will be transmitting the repeated HARQ-ACK during this next time interval; as a result, peak throughput is reduced.